diff --git a/sympy/physics/hep/gamma_matrices.py b/sympy/physics/hep/gamma_matrices.py
index 23284e4a92..8869cc7a8f 100644
--- a/sympy/physics/hep/gamma_matrices.py
+++ b/sympy/physics/hep/gamma_matrices.py
@@ -695,7 +695,8 @@ def kahane_simplify(expression):
     # If `first_dum_pos` is not zero, it means that there are trailing free gamma
     # matrices in front of `expression`, so multiply by them:
     for i in range(0, first_dum_pos):
-        [ri.insert(0, free_pos[i]) for ri in resulting_indices]
+        for ri in resulting_indices:
+            ri.append(free_pos[i])
 
     resulting_expr = S.Zero
     for i in resulting_indices:
